Various physiologic signals are often recorded and analyzed. These signals may included digestive pH, various digestive motility and pressure signals, EEG and EMG, signals, and so on.
Typically, physicians require the concurrent recording a variety of physiologic signals. For example, gastric pH is often collected at the same time as pressure. Through the concurrent collection of various parameters the physician may better understand the patient's condition.
Ambulatory recording and recorders are widely used to collect such data. Such devices include the Digitrapper Mk III.TM. ambulatory recorder from Synectics Medical AB, the GastroScan II.TM. from Medical Instruments Corporation, and the SuperLogger.TM. from Sandhill Scientific. These types of devices make it possible for patients to remain at home, or at least to be ambulant in a hospital setting while physiological data is recorded. Typically the devices comprise a lightweight recorder in which the desired physiological data signals are temporarily stored and later downloaded for future analysis.
Many types of physiological data may be recorded, including ECG (Electrocardiogram) data, EEG (Electroencephalogram) data or pH and pressure data (Motility) in the gastrointestinal tract. Preferably such a recorder should be able to record among a programmable number of channels at a variety of programmable frequencies.
Among the problems with current recorders, however, is that of energy usage. Such recorders, because they must be ambulatory, are battery powered. Thus an ambulatory medical recorder must minimize energy usage while performing almost constant sampling across a variable number of channels at one or more frequencies.
One approach to limit power consumption, while still permitting an enhanced graphical user interface, is to equip the device with two microprocessors. A first, real time processor for sampling, which operates with a relatively low current drain, and a second, non time processor for permitting an enhanced graphical user interface are employed.
Such a device, comprising a real time sampling processor, volatile memory, and a non real time operating system processor, and a non-volatile memory must, however periodically transfer the data collected in the volatile memory to the non-volatile memory.
Typically such a device samples and collects data during specific processor power on or "awake" cycles. One problem which may arise during such data transfer is when the device samples along several channels and the volatile memory becomes filled before all the channels to be sampled at a particular time are actually sampled. That is, if a memory buffer is filled during a tick before all the channels are sampled, then the remaining data which should be collected is not collected and is thus lost.